Portable electronic devices, such as those configured to be handheld or otherwise associated with a user, are employed in a wide variety of applications and environments. The ubiquity of such devices as mobile phones, tablets, digital still cameras and video cameras, handheld music and media players, portable video game devices and controllers, mobile internet devices (MIDs), personal navigation devices (PNDs), smart watches, smart glasses, belt clips or other wearables, and other similar devices indicates the popularity and desire for these types of devices. Increasingly, such devices are equipped with one or more sensors or other systems for determining the position or motion of the portable device, including inertial navigation techniques based upon the integration of specific forces and angular rates as measured by inertial sensors (e.g. accelerometer, gyroscopes).
Often, such portable devices may be associated with a platform that transports the device, as in the example of a mobile phone being carried by a user. Further, many situations exist in which the motion of the platform exhibits periodic characteristics. This may include on foot motion of the user, such as walking, running and other similar forms of locomotion involving the periodic repetition of steps. Similarly, other types user activity may also exhibit periodic motion characteristics, including swimming, biking, skiing, rowing and others. Additionally, the user of the portable device or the portable device itself may be associated with a platform other than the user that nevertheless exhibits periodic motion characteristics, such as horseback riding.
Although the portable device generally may be transported in the direction of movement of the platform, its orientation may not be constrained, resulting in a misalignment of a heading determined for the device with the platform heading (direction of motion or direction of the along-track movement of the platform). As in the example of a mobile phone, it may be held in the user's hand and employed in a variety of orientations or carried in a pocket, holster, bag or other manners.
In contrast, traditional systems typically involve a device tethered to the platform so that measurements from the device may be used to determine the position, velocity and attitude of the device and/or the platform. For example, alignment of the inertial sensors within the platform (i.e. alignment of the device containing the sensors with the platform's forward, lateral and vertical axis) may be required for traditional inertial navigation systems, such that when the inertial sensors are not properly aligned, the positions and attitude calculated using measurements from the inertial sensors are not necessarily representative of the state of the platform. Thus, traditional systems achieve high accuracy navigation solution by tethering the inertial sensors within the platform with accurate aligning of the device axes with respect to platform axes. As noted, mobile or portable devices can be moved, whether constrained or unconstrained within the platform (such as for example a person, vehicle, or vessel of any type), and careful mounting or tethering of the device to the platform is not an option.
Accordingly, existing portable devices having navigational capabilities may achieve accurate attitude and position of the platform under at least one of the following three conditions of known information:    1) absolute attitude angles for the device and the platform;    2) absolute attitude angles for the device and the misalignment between the device and platform;    3) absolute attitude angles for the platform and the misalignment between the device and platform.Thus, it will be appreciated that knowledge of misalignment may enable navigation techniques for a portable device without requiring separate assemblies of sensors for the device and the platform.
In addition to sensor-based inertial navigation systems, a portable device may also be equipped with reference-based position determination systems. As one example, a portable device may utilize a Global Navigation Satellite System (GNSS), such as Assisted Global Positioning System (AGPS) system having high sensitivity capabilities capable of providing absolute positioning of the platform (e.g. user) even in environments without a clear line of sight to satellite signals. Nevertheless, in some situations, GPS information alone may be inadequate enough, such as deep indoors or in challenging downtown navigation or localization. Other reference-based position determination systems may rely on cell tower identification or, if possible, trilateration of cell towers or other wireless communication signals to obtain a position fix to supplement a GPS system or to be used in the alternative.
Despite these and other known positioning methods available in many portable devices, accurate indoor localization still presents a challenge and may be inadequate to satisfy the accuracy demands of current location based services (LBS). Additionally, these reference-based methods may only provide the absolute heading of the platform, without any information on the device's heading.
Therefore, there is a need for portable device navigation techniques capable of accurately utilizing measurements from an inertial sensor assembly of the portable device within a platform, and thereby determining the navigation state of the device and/or platform without any constraints on the platform (i.e. in indoor or outdoor environments) or the orientation of the portable device with respect to the platform. In one aspect, this may include estimating heading misalignment between the portable device and the platform. There is a further need for making such determinations in a manner that is independent of the usage of the device (e.g. the way the user is holding or moving the device during navigation). Similarly, it would be desirable to make such determinations without requiring the orientation of the portable device to be constrained with respect to the platform. The following disclosure satisfies these and other needs.